Patent Number: 6,252,930

Title: Method and apparatus for measuring thickness of coating layers on substrates using backscattering of x-rays and gamma rays

Abstract: The present invention provides a method and apparatus for non-destructive, in situ measuring thicknesses of layers on substrates. The method and device uses a probe including a radioactive source in a source holder and a photodetector mounted behind the source for detection of backscattered photons. In one aspect the method is used to measure the thickness of paint deposited onto metal substrates. The source holder and photodetector array forms a cylindrically symmetric probe for producing an axially symmetric beam of primary photons. A source containing radioactive .sup.109 Cd producing high energy photons of energy 22 and 25 keV is spaced from the painted surface so the photons impinge on the painted substrate. The intensity of photons backscattered by Compton scattering in the paint layer is proportional to the mass density of the paint to give a direct measurement of the paint thickness. The photons penetrating through to the substrate are absorbed within the substrate. The device also provides a method for calculating the distance from the source holder to the substrate using backscattering of gamma rays.

Inventors: MacKenzie; Innes K. (Guelph, CA)

Assignee: University of Guelph

International Classification: B64D 15/00 (20060101); B64D 15/20 (20060101); G01B 15/02 (20060101); G01B 015/02 ()

Expiration Date: 06/26/2018